The proposed research is designed to investigate the relationship between renal sodium transport and intrarenal hemodynamics with particular reference to an experimental model of renal sodium retention and hyperaldosteronism; namely, dogs with chronic constriction of the thoracic inferior vena cava and ascites (caval dogs). Intrarenal blood flow distribution will be assessed by the Xenon-133 washout method combined with autoradiography and sodium and water excretion will be measured by classical clearance methodology. Normal and caval dogs will be examined under baseline non-diuretic conditions and following acute alterations in sodium and water excretion induced by saline loading (volume expansion) or the administration of angiotensin II, propranolol, phenoxybenzamine and various diuretics. Experiments will be performed under maximum hydropenic conditions or during water diuresis so that the site of action of the various agents may be assessed by the observed alterations in free water reabsorption and free water clearance, respectively. Correlations will be made between sodium and water excretion patterns and patterns of blood flow distribution, with emphasis on contrasting normal and caval dogs during the non-diuretic control state and following the induced alterations in sodium excretion.